The present invention relates generally to fireworks and, more particularly, to a fireworks aerial display shell, such as a consumer fireworks aerial display shell, of the type intended to be launched from a launch tube of a mortar and to a method of launching the aerial display shell to a desired altitude where it breaks or bursts to create a pyrotechnic, visual effects display.
As used herein, “consumer fireworks” has the meaning set forth in Title 27, Code of Federal Regulations, Section 55.11, as small fireworks devices designed to produce visible effects by combustion and which comply with the construction, chemical composition, and other requirements of the U.S. Consumer Product Safety Commission, as set forth in Title 16, Code of Federal Regulations, parts 1500 and 1507.
Consumer fireworks aerial display shells of the type intended to be placed within and then launched from a launch tube of a mortar are well known and are commonly referred to as reloadables. An example of one such aerial display shell is disclosed in U.S. Pat. No. 6,912,958. The aerial display shell disclosed in that patent has a cylindrical casing and a long lead fuse, commonly referred to as a shell leader, that ignites a lift charge housed at one end of the casing. When ignited, the lift charge propels the aerial display shell upwardly and out of the launch tube. The aerial display shell includes an effects charge, comprised of stars and a burst charge, which is separated from the lift charge in the casing and produces the pyrotechnic visual effects display. The effects charge is ignited by a timing or delay fuse. The timing fuse is ignited by the burning lift charge and burns while the aerial display shell is being propelled through the length of the launch tube and during its upward ballistic travel outside the launch tube. The burn time of the timing fuse is set to allow fire to be communicated to the effects charge once the aerial display shell has reached or nearly reached the apex in its ballistic trajectory.
When the aerial display shell described above is properly placed within the mortar, the lift charge is at the bottom of the launch tube and the effects charge is positioned above the lift charge. When oriented in this manner, the hot product gases of the ignited lift charge exert a force against the bottom of the aerial display shell and propel the aerial display shell upwardly out of the launch tube through its open top. It sometimes happens that a user will inadvertently place an aerial display shell within a launch tube in an inverted orientation, with the lift charge positioned above the effects charge. When placed in this orientation, the hot product gases of the burning lift charge do not act upon the aerial display shell to propel it out of the mortar but are instead uselessly vented through the open top of the launch tube. As a result, the aerial display shell remains resting on the closed bottom of the launch tube as the timing fuse continues to burn and then ignites the effects charge while the aerial display shell is inside the launch tube rather than at a safe altitude above the mortar. When the effects charge ignites inside the launch tube, the hot product gases produce an overpressure which can cause the mortar to be ruptured. One approach to reducing the potential hazard to users and spectators in the immediate vicinity of the launch tube is to strengthen the launch tube with a reinforcing sleeve that helps the launch tube to withstand the explosive force of the effects charge, such as is disclosed in U.S. Pat. No. 8,807,037.
While the sleeve as disclosed in U.S. Pat. No. 8,807,037 helps to prevent outward rupturing of the tubular wall of the launch tube, the explosive force of the ignited effects charge may still cause the closed bottom or base plug of the launch tube to rupture, making the launch tube unsuitable for reuse. Thus, there remains a need for further improvements that reduce the opportunity for damage to launch tubes and injury to users and spectators when an aerial display shell is loaded in the launch tube in an inverted orientation.